There are various kinds of liquid crystal display (LCD) such as TN, STN, IPS and FFS, depending on the characteristics of an LCD panel and a voltage application mode, and the liquid crystal display is prepared usually by combining 7-20 kinds of single liquid crystal compounds, since it is impossible with one or two materials to adapt the characteristics thereof to those required for a product such as temperature of a clearing point, dielectric anisotropy, refractive index anisotropy and rotational viscosity. The characteristics required for this liquid crystal composition are as follows:
TABLE 1Characteristics of liquid crystal mixture required for LCDCharacteristics of liquid crystalCharacteristicDevice parameter changemixturevaluesRemarksdue to liquid crystalStability at low temperature (° C.)−20° C. or lesssmaller the betteroperating temperaturecharacteristicClearing point (° C.)70° C. or morelarger the betteroperating temperaturecharacteristicDielectric anisotropy (positive2 or morelarger the betterthreshold voltage,value)characteristicresponse timeRefractive index anisotropy0.07 or morevaried with a deviceluminanceRotational viscosity (mPas)as low as possiblesmaller the betterresponse timecharacteristicModulus of elasticity8~18 pNvaried with a deviceresponse time, threshold(average value of K11, K22, K33)voltage, luminance
A single liquid crystal compound forming this liquid crystal composition is an organic material having a molecular weight of 200-600, which has a molecular structure of a long bar shape. The structure of the single liquid crystal compound is divided into a core group maintaining straightness, a terminal group having flexibility, and a linkage group for a specific use. The terminal portion includes an easily bendable chain form (alkyl, alkoxy, alkenyl) at one or both ends to maintain flexibility, and a polar group (F, CN, OCF3, etc.) introduced at the other end to serve to adjust the physical properties of a liquid crystal such as a dielectric constant.
As it has been several decades since a single liquid crystal compound applied to a liquid crystal display (LCD) technology was developed, various forms of single liquid crystal compound are being prepared, and liquid crystal compositions are being prepared by combining these single liquid crystal compounds, however, there is still a continuous demand for a liquid crystal composition having best performance of a liquid crystal display (LCD).
As a single liquid crystal compound related to the present invention, a fluorine-substituted terphenyl compound of Chemical Formula 1 is disclosed in Japanese Patent Laid-Open Publication No. 1993-025068, a representative non-polar liquid crystal compound having two cyclohexanes linked to each other is disclosed in European Patent Application Publication No. 0122389, and a plurality of fluorine-substituted liquid crystal compound being advantageous for improving dielectric anisotropy are disclosed in Japanese Patent Laid-Open Publication No. 1990-004724; however, only the properties of each liquid crystal compound are known in the art, and a formulation technique for a liquid crystal composition having easily adjustable rotational viscosity while maintaining other performance in an optimal condition, under complex interactions of stability at low temperature, a clearing point, dielectric anisotropy (positive value) and rotational viscosity adjustment, in recently commercialized various liquid crystal displays (LCD), is not known in the art.